A failed firmware update can brick your router (turn it into an expensive paperweight). Follow this checklist to minimize risks.
Log in to your router and go to System Status to note your current version. Tenda D305 Firmware Update
Log in to your router (usually at 192.168.1.1 ) and check the current System Version under the Advanced or System Status page to ensure you actually need an update. A failed firmware update can brick your router